Lice are blood-sucking insects and specific parasites of human beings. Lice are 1-3 mm long and have three pairs of legs that end in powerful claws.
- Pubic lice are slightly smaller than head lice and body lice.
- The female lives for 1-3 months but dies when separated from the host. The female louse lays up to 300 eggs, called nits, during her lifetime.
- The nits are less than 1 mm in diameter and, when viable, are opalescent. The nits hatch 6-10 days after laying, giving rise to nymphs that become adults in 10 days.
3 species of lice have adapted to live on humans:
- Head louse (Pediculus humanus capitis) - see separate article Head Lice.
- Crab (or pubic) louse (Pthirus pubis) - see Pubic lice section (below).
- Body louse (Pediculus humanus).
The pubic louse (Pthirus pubis) is 'crab'-shaped, grey-brown in colour, and about 2 mm in length. The female lays eggs (smaller than a pinhead) on the hair shaft, near to the body. The eggs hatch after about 6-10 days. The empty eggshells (nits) are tightly attached to the hair. The female louse lives for 1-3 months. Eradication of pubic lice from the body is unlikely unless treated.
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- They are common among young adults.
- Pubic lice are transmitted by close body contact, which can be from sexual contact or from close family contact (eg from an infested beard or chest).
- Pubic lice in children may be an indication of sexual abuse but most children with pubic lice infestation have probably acquired this innocently.
- The incubation period is usually between 5 days and several weeks.
- The diagnosis is based on finding adult lice or eggs. Pubic lice live on coarse hair, especially in the pubic and perianal areas, but also on the eyelashes, abdomen, back, axillae and on the head. Therefore, all hairy parts of the body should be examined. A fine-toothed comb may be useful for detection.
- Itchy red papules are the most common presentation. Itching takes 1-3 weeks to develop after the first infestation, but may occur immediately following reinfestation. Itching tends to be worse at night.
- Blue macules may be visible at feeding sites.
- Minute dark-brown specks of louse excreta are sometimes seen on the skin and underwear.
- Nits: seborrhoeic scales, small crusts of scratched dermatitis, hair muffs (secretions from the hair follicle that are wrapped round the hair shaft). These can all be brushed off but nits are firmly attached to the hair.
- Body (clothing) lice (Pediculus humanus), which are slightly larger than pubic lice , and found only on clothes; head lice (slightly larger than pubic lice and found only on the scalp).
- Itchy red papules: scabies.
- Consider whether the pubic lice infestation has been acquired via sexual or nonsexual contact.
- If acquired via sexual contact, refer to a genitourinary medicine (GUM) clinic for treatment, screening for other sexually transmitted infections, and contact tracing.
- Treat the individual with a topical insecticide: two applications of malathion 0.5% aqueous lotion or permethrin 5% dermal cream, 7 days apart. All surfaces of the body should be treated, including the scalp, neck, and face (paying particular attention to the eyebrows and other facial hair).
- Advise the individual to avoid close body contact until they, and any current sexual partner, have been treated.
- Any close contacts over the past 3 months should be examined for pubic lice.
- For people with infestation of the eyelashes, treat the eyelashes with an inert occlusive ophthalmic ointment (eg simple eye ointment BP) or a topical insecticide (a cream rinse or shampoo should be used). An inert occlusive ophthalmic ointment should be used for people under the age of 18 years, and for those who are pregnant or breast-feeding.
- If pubic lice infestation is unresponsive to initial insecticide treatment, repeat the previous treatment with the correct technique (rather than switching to a different treatment).
- If insecticide resistance is suspected, switch to the alternative insecticide (malathion or permethrin).
- When reinfestation occurs, repeat the previous treatment; assess all close contacts for pubic lice and treat all positive cases simultaneously.
- Excoriation and skin infection due to scratching.
- Blepharitis, conjunctivitis, or corneal epithelial keratitis when the eyelashes are affected.
- Shaving the infested areas does not provide protection from reinfestation because pubic lice need only a minimal length of hair on which to lay eggs.
- Pediculosis is usually caused by contact with an infested person.
- Body lice are most often seen in cold climates, in poor sanitation and with overcrowding.
- Body lice also occur mainly when clothes are not changed or washed regularly. Therefore homeless populations are predominantly affected.
- Pediculosis and scabies may coexist in the same individual.
- Patients usually present after discovering lice or nits.
- Many lice infestations are asymptomatic.
- Pruritus is accompanied by excoriations that can become infected secondarily and papules linked to bite reactions.
- Diagnosis is based on seeing eggs (nits), nymphs or mature lice. Observing lice is difficult. Nymphs and mature lice, despite being unable to hop or jump, can move rapidly through dry hair. The use of a magnifying glass assists with diagnosis.
- Mature lice are 3-4 mm long. Nits are much smaller (about 1 mm). The pubic louse is about the same length as the head or body louse but has a wider body.
- Body lice can be found in any area of the body, although they tend to avoid the scalp, except at the margins. Nits are laid in the host's clothing and are not usually found on the hair as with head lice and pubic lice. Body lice and eggs are found in clothing seams.
- Chronic infestation often leads to postinflammatory pigmentation.
- Unlike dandruff and hair root sheath casts, nits are stuck to the hair and are difficult to remove.
- Nits are fluorescent under a Wood's light.
Treatment includes improved hygiene and laundering in hot water of all the infested clothing, bedding and linens. Drug treatment (eg malathion or permethrin) is required in large-scale infestations.
- Bedlinens and clothes must be systematically decontaminated.
- Hygiene and washing clothes, bedding and towels are most important and are usually sufficient but application of permethrin or malathion may be required.
- Outbreaks require delousing of people with 1% permethrin dusting powder, basic sanitation and hygiene, changes of clean clothing, and sometimes shaving.
- Antibiotics are needed to treat louse-borne infectious diseases.
- Treating clothing with permethrin may prevent infestation.
- Treatments are very effective in killing nymphs and mature lice but less effective in killing eggs.
- Appropriate therapy produces a cure in more than 90% of cases.
- To prevent reinfestation, treat contacts of the patient at the same time as the patient.
- Washing combs and brushes reduces reinfestation.
Further reading & references
- Pubic lice, Clinical Knowledge Summaries (2007)
- Management of pediculosis pubis, British Association for Sexual Health and HIV (2007)
- British National Formulary
- Nutanson I, Steen C, Schwartz RA; Pediculosis corporis: an ancient itch. Acta Dermatovenerol Croat. 2007;15(1):33-8.
- Chosidow O; Scabies and pediculosis. Lancet. 2000 Mar 4;355(9206):819-26.
- Bechah Y, Capo C, Mege JL, et al; Epidemic typhus. Lancet Infect Dis. 2008 Jul;8(7):417-26.
|Original Author: Dr Colin Tidy||Current Version: Dr Colin Tidy|
|Last Checked: 25/08/2010||Document ID: 2991 Version: 23||© EMIS|
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